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FROM BULLETIN OF THE UNITED STATES BUREAU OF FISHERIES : VOLUME XXXII. 1912 
Document 787 ::::::::::::: Issued February 18, 1914. 



THE OXYGEN REQUIREMENTS OF SHELLFISH 



By Philip H. Mitchell 



16284" — J4 



207 






d; of d. 

fif*Aii 4 5914 



THE OXYGEN REQUIREMENTS OF SHELLFISH. 

By PHILIP H. MITCHELL. 

The respiratory exchanges in lamelUbranchs seem not to have been investigated. 
Probably the most notable work related to it is that of Vernon." He measured the oxy- 
gen utilization and carbon dioxide emission in a large number of marine forms, including 
certain MoUusca but no lamellibranchs. He showed that in the lower marine forms 
investigated, including Coelenterata, Tunicata, and Mollusca, the respiratory exchange 
was very small compared to the higher ones, for example, teleosts. There were, however, 
certain exceptions to this rule, notably the protozoan Collozoum inerme, which showed 
nearly as high a respiratory exchange as the fishes. He found also that, in general, the 
respiratory activity was more readily responsive to temperature in the lower than in 
the higher forms. He further showed that the gaseous exchange was relatively greater 
in the small than in the large individuals of the same species and found that, in general, 
the same distinction held between small and large species. The transparent pelagic 
animals were shown to have a very small proportion of soUd organic matter in their 
tissues, so that calculated on that basis their respiratory activity was very large, greater 
indeed than fishes, amphibians, or even mammals. 

In the present work some of those findings have been confirmed for the lamelli- 
branchs. They show a ready responsiveness to temperature changes, a smaller utili- 
zation of oxygen in proportion to the body weight with increase in size, and those forms 
which showed a low oxygen requirement in relation to their entire weight showed a 
higher utilization in proportion to their dried weight. 

The resistance to lack of oxygen in forms which have no power of locomotion is 
an important factor in adverse conditions. This is especially true of the edible shellfish, 
which, because of enforced closure during cold weather, or in the presence of polluted 
or roily water, or in water whose oxygen has been lowered by the presence of certain 
wastes or an abundance of life, must at times be deprived of their normal supply of 
oxygen. The subject therefore possesses an economic significance, and it was, in fact, 
the possibility that certain manufacturing wastes, removing oxygen from sea water, 
might therefore cause the death of oysters and clams which first directed the writer's 
attention to the subject. The particular wastes involved were those of gas works con- 

f Vernon. H. M.; Respiration in marine forms. Journal of Physiology, vol. XIX, 1895, p. 18. 

209 



2IO BULLETIN OF THE BUREAU OF FISHERIES. 

taining at least traces and sometimes significant quantities of water-gas tar and other 
oily matter. The results of this investigation indicate, in a word, that the tar or oily 
wastes could have no effect on shellfish in this way. The details of this part of the work, 
however, are reserved for a report dealing specifically with the effect of water-gas tar on 
oysters. This paper is confined to oxygen requirements of shellfish and their resistance 
to lack of oxygen. 

METHOD OF EXPERIMENT. 

The method of manipulation was, in brief, to place the shellfish in a desiccator 
completely filled with sea water of known content of dissolved oxygen, leave the apparatus 
at some constant temperature during a definite period, and then to sample the water 
in the desiccator so as to compute its decrease in dissolved oxygen. Winkler's well- 
known titration method was used to measure the oxygen both at the beginning and end 
of each experiment. A vacuum desiccator was used for the containing vessel because 
it could easily be closed water-tight, could accommodate almost any size of shellfish, 
and enabled one to take through the side opening with glass stopcock a fair sample of 
the contents. 

In practice a number of precautions were found necessary. The hollow dome of 
the desiccator cover was entirely filled with paraffin to exclude air from entrapment 
in it. A glass tube within the desiccator was connected to its side stopcock and reached 
nearly to the bottom. When, therefore, the filled desiccator was opened at the top 
water could be sucked off through the opened side cock into the sampling bottle so that 
the sample would come from a point well below the surface of the water, where the oxy- 
gen content would be fairly constant. The sea water " used in each experiment was 
brought to the required temperature and placed in a large reservoir jar on a shelf, from 
which it could be siphoned without bubbling into the desiccator. When it was thus 
nearly filled, an oyster was gently placed on a glass tripod, where it would rest near the 
center of the desiccator. With clams it was found necessary to leave them in the 
desiccator submerged in water for a few hours before the experiment, because, unlike 
oysters, they would not open quickly after they had been handled. In either case, 
though, water from the shelf reservoir was siphoned into the overflowing desiccator for 
sufficient time to bring the oxygen content to approximate constancy and then the 
cover was put on, leaving just opening enough to admit the siphon tube. 

The side cock of the desiccator was then connected by rubber tubing to the sampling 
bottle, and after starting by suction the water was allowed to siphon through the bottle 
two to three minutes. This period was found quite sufficient to give reliable duplicate 
results for water containing any percentage of oxygen measured in these experiments. 
The water running into the desiccator meantime was in excess of that running into the 
bottle, so that an overflow was maintained from the top of the desiccator and the sample 
rendered as fair as possible. At the exact second recorded as the beginning of the experi- 
ment the side stopcock was closed, the siphon quickly withdrawn from the desiccator, 

" From aquarium of running sea water, a part of the aquarium system of the laboratory. 



OXYGEN REQUIREMENTS OF SHELLFISH. 211 

and its lid put completely on, excluding bubbles. The entire apparatus was then kept 
in a bath of sea water whose temperature was maintained approximately the same as the 
water within the desiccator. The oxygen in the sample was meantime measured by 
titration. 

After a period, usually about an hour in lengthy the desiccator was two or three times 
inverted to render its contents uniform and to stimulate the shellfish to close and thus 
stop using oxygen. The exact time of the first rough movement of the apparatus was 
recorded as the closing time of the experiment. The outside of the desiccator was then 
dried with a towel and the entire apparatus weighed. When currents in the water had 
come practically to rest, the side stopcock was again connected to the same sampling 
bottle used at the beginning of the experiment and a sample taken as before. Since 
the capacity of the desiccators was sufficient for 1,200 grams of water, even with the 
large shellfish, and as the sampling bottles held approximately 300 grams, it is plain 
that water could run through the sampling bottle some time without emptying the 
desiccator. The stream indeed was allowed to run at least two minutes. The capacity 
of the desiccators was not enough to permit of taking a duplicate sample that would be 
reliable, but this was not necessary because there is little chance of error in the Winkler's 
titration. 

The last step in the process was to empty the desiccator completely, dry it and the 
shellfish, and weigh them together. This gave a means of determining by difference the 
weight of the water. It was probably accurate to within 2 grams. As the dissolved 
oxygen of the water both at the beginning and the end of the experiment was calculated 
in parts per million, it was only necessary to multiply the weight of water used by the 
decrease in its oxygen content expressed in parts per million and divide the result by 
100 to find the decimilhgrams of oxygen used by the shellfish. Experiment showed that 
no correction for change in the oxygen content of the water due to microorganisms or 
physical factors was, under the circumstances of constant temperature, etc., necessary. 
Results were expressed in decimilligrams of oxygen per hour and in most cases also com- 
puted in decimilligrams per hour per 100 grams of shellfish and in some cases in decimil- 
ligrams per hour per i gram of the dried weight of the total shell contents of the organism. 

A formula for the first of these three computations might be expressed, therefore, as 

follows : 

,a'-a" 60 



A=W- 



100 / 



where A is the decimilligrams of O used per hour, W the weight, in grams, of water in the 
desiccator, a' the parts per million of oxygen in the first sample and a" in the second 
sample, and t is the time of the experiment in minutes. 

Throughout the experiments it was found necessary to observe the animal at fre- 
quent intervals, and if the shells closed up to discard the experiment, or if the shells 
closed only after a considerable number of minutes had elapsed to terminate the experi- 
ment immediately. This precaution was necessary because, as is well known, certain 
of the shellfish used in this work can close water tight and in that condition take from the 



212 BULLETIN OF THE BUREAU OF FISHERIES. 

water, as will be shown below, no oxygen except the very small amount absorbed by 
their shells. 

It appeared early in the work that constancy of results was exceedingly difficult to 
obtain. This was due to a variety of causes, chief of which was the great variability in 
the openness of the shells, for not only could the oyster or clam entirely or at least 
obviously close so that the experiment had to be terminated, but it could partially and 
unnoticeably close or indeed fail to open wide even from the beginning of the experiment. 
For the oyster, at least, the author succeeded in demonstrating this by graphic records. 
One shell of an oyster was connected by tying a string to the projections with a lightly 
balanced lever recording on a slow kymograph. As soon as the oyster in a water bath at 
a temperature between i8° and 20° C. had opened somewhat, the kymograph was started 
and the temperature of the bath raised at the rate of 1° C. in about eight minutes. The 
oysters remained fairly well open with brief periods of partial closure as the temperature 
increased to about 22° C. At that point there invariably appeared in the three individ- 
uals observed periods of maximum openness lasting as long as no disturbing factor inter- 
vened. Suificient stimulus for partial closure, however, was likely to occur frequently. 
A light tap on the table or water bath, a heavy step in the room, the slamming of a door 
in a neighboring part of the building, or, indeed, any slight jar was surely registered by 
some movement of the shell. As the temperature increased up to about 26° or 27° C, 
the effect of these stimuli was much less marked. The oysters then maintained their 
maximum openness very persistently. Between 27° and 30° a tendency to very slow 
and incomplete opening after closure was noticeable, indeed no maximum openness was 
seen. At about 30° or 31° C, the oysters closed tightly, even if no mechanical stimulus 
was g^ven. 

As the kymograph method served to detect movements of the shell not noticeable 
to unaided observation and also slight openings of the shell not otherwise visible, these 
experiments were an aid to planning and interpreting measurements of oxygen utiliza- 
tion. They showed that below 19° C. and above 26° C. observations on the opened 
oyster were impossible, that temperature must be maintained constant throughout the 
experiment, and mechanical disturbances must be avoided as far as possible. A further 
source of difficulty had also to be overcome. When the oyster excreted it closed vio- 
lently, to drive the fecal matter out of the shell. If the position of the animal rendered 
complete excretion difficult, closures were frequently repeated, and sometimes the oyster 
shut up tightly. It was necessary, therefore, to lay the oyster in the desiccator tipped 
so that the more concave side of the shell, where excretion occurs, would be lower than 
the other. 

In spite of all precautions, however, perfectly consistent results could not always 
be obtained. Under the same or comparable conditions of temperature, oxygen content 
of the water, and physical conditions, the same individual would sometimes in different 
experiments give results disagreeing beyond the limits of the calculated, probable, experi- 
mental error. Various observations make it seem likely that the nutritive condition 
of the individual could account for some, at least, of these discrepancies. Thus, after 



OXYGEN REQUIREMENTS OP SHELI.FISH. 213 

remaining at a high temperature (e. g., 24°-26° C.) for some time, the oxygen require- 
ment at a slightly lower temperature would tend to be greater than if the shellfish had 
been at a lower temperature before the experiment. If an oyster had been out of water 
for some time before the measurement, more oxygen would be used, generally, than if 
the specimen were left in the aquarium until the time of the experiment. After the 
shellfish had been kept in the aquarium some weeks they tended to use less oxygen 
than when taken recently from their native environment. Exceptionally an individual 
would show a high utilization of oxygen out of proportion to previous measurements 
and lasting for several days. As many of the interfering conditions as possible were, 
of course, eliminated, but still it seemed necessary to make a considerable number of 
experiments and draw conclusions only from averages. More than 350 measurements 
were made under various conditions on three types of lamellibranchs — the oyster (Ostrea 
virginica), the soft-shell or long clam {Mya arenaria), and the quahog or round clam 
{Venus mercenaria). 

RESULTS. 

OXYGEN REQUIREMENTS OF THE OYSTER. 

Three series of experiments, each made on a limited number of individuals, are sub- 
mitted. Although the results can scarcely be taken to show any seasonal variation, 
they are grouped, for convenience, according to the time they were carried out. In 
table I are the results of measurements taken during July, 191 1; in table 11, those of 
July and August, 1912; and in table ill are results obtained during the latter part of 
August, 1912. 

In the experiments of table i definite temperatures were not previously chosen and 
carefully adhered to as in the later work. The results, therefore, are here grouped for 
comparison as follows : All measurements taken at temperatures between 20° and 2 1 .3° C. 
appear in one column, those at 21.5° to 23.5° C. in another, and those between 26° and 
28° C. in a third. Where two or more experiments were made with one oyster at tem- 
peratures within a given range the average of the results is placed in parentheses. . In 
the last three columns are the averages of comparable experiments computed as the 
decimilHgrams of oxygen used per hour per 100 grams of oyster. By weight of oyster 
is meant in this and other tables not otherwise specified the weight in grams taken after 
it was closed under water, wiped as dry as possible with a towel, and left to dry in the air 
not more than half an hour. Such weighings were shown by duplication to be accurate 
to within two-tenths of a gram. 

In table 11 are the results of experiments performed at definite chosen temperatures 
so controlled that the variation was not more than half a degree centigrade in any single 
experiment. The first five columns of results show the decimilHgrams of oxygen used 
per hour at five temperatures by nine oysters. The averages of all comparable experi- 
ments are put in parentheses. The last five columns contain the averages, expressed 
in decimilHgrams, of the oxygen used per hour per 100 grams of oysters. 



214 BULLETIN OF THE BUREAU OF FISHERIES. 

Table I. — Oxygen Used by Oysters. 

Note.— Figures in parentheses are averages of experiments under approximately uniform conditions. 



Weight 


Decimilligranis of oxygen used 
per hour. 


Average decimilUgrams of oxygen 
per hour per 100 grams of oyster. 


of whole 

oyster. 


At 20" to 


At 21.5" to 
23-5° C. 


At 26° to 
28° C. 


At 20° to 
21.3° C. 


At 21.5* to 
23.5° c. 


At 26° to 
28° C. 


Grams. 

43.0 

56.6 
85.0 

106.0 

113- 

137.0 

141. 




5-6 
9.0 
7-8 
6.8 
(7.3) 

II. 8 
7.6 
(9-7) 






17.4 
17.2 












9.4 
14.7 

14.0 

(13.7) 

10. 1 
15-6 
(12.8) 

14.6 

12.7 
13.6 


19-3 
18.8 
(19..) 

22.9 
22.9 
26.2 
(24.0) 


14-9 
12. z 
12.9 

II. I 


22.4 
22.6 


19.4 

18.2 
16. 1 
(i7-i) 

21.8 
21. s 
19.0 
21. 2 
(20.9) 

19.0 
18.0 

(1S.5) 


18.3 

15- 1 
16. s 

13-1 



















OXYGEN REQUIREMENTS OF SHELLFISH. 
Table II. — Oxygen Used by Oysters. 

-Figures in parentheses are averages of measurements under approximately uniform conditions. 



215 



Weight 
«t whole 


Decimilligrams of oxygen 


used per hour. 


Decimilligrams of oxygen used per hour per 100 
grams. 






















oyster. 


At 19.5° 
to 20° C. 


At 21° to 
21.3° C. 


At 22° to 

22.5° c. 


At 24° to 
2A.sC. 


At 26° to 
26.3° C. 


At 19.5° 

t0 20°C. 


At 21° to 
21.5° c. 


At 22° to 

22.5° C 


At 24° to 
24.5^ c. 


At 26° to 
s6.s°C. 


Grams. 

42.0 


;. 6 
9.8 

(8.7) 


12.3 

13-8 

(13.1) 


10.3 

13.9 

(12.2) 


14.6 


13.4 
14.9 
II. 2 
(l3-l) 


20.; 


31.0 


.'9- I 


34-8 


31.3 


51.0 


II. 6 
10. 7 
II. 8 
(11.3) 


9-3 
II. 4 
9-5 
6.2 
(9-6) 


u. 7 
II. s 
(II.6) 


12.6 

12.7 
(12. 6s) 


13-6 


22.2 


17.9 


22.8 


24-8 


25. 7 


66.5 


.5-. 

9.4 
10.5 

9.1 
(11. 2) 


16.0 
9.9 

16. I 
14- 
(14.0) 


15.5 
II. 8 
(■3.7) 


16.0 


18.6 
17.2 
(17.9) 


16.9 


21.0 


20.6 


24. I 


26.9 


;6.o 


II. 5 
14.0 

(12.7) 


13.9 
15-3 
14-2 
(14. s) 


■53 

12.8 
(14.0s) 


is.s 

20. s 
16.2 
(17-5) 


23- S 
20.9 
24.5 
20. 7 
(22.4) 


16.7 


19.0 


18. s 


23.0 


29. S 


97-4 
uS. 


13.4 

13-7 
17.S 
(■S.7S) 


14.6 








13.8 






1.9.5 




17-9 
25.9 
18.6 
18.4 
(20.2) 


25.9 
19.8 
(22. 8) 


24.8 


12.3 




15- 7 


17-8 


19.4 






147.0 


16.0 
19.4 
(.7.7) 


iS. 4 

18.2 
(18.3) 


20.4 
19.3 
(19.8) 


20.8 
21.9 
(21.3) 


26.6 
26.0 
(26.3) 


12. I 


12.5 


13-5 


14. S 


17.9 


344.0 


18. I 
22.3 
(20.2) 


23.5 

25- 7 
(24.6) 


34.6 


30.0 
26.1 
24.0 
(26. 7) 


35- I 


8-3 


10. 1 


12.3 


II. 


14.4 


2&1.0 


19.0 


29.1 
29.5 
21.4 

20.8 

(25.2) 


27.4 
24.8 
(26.1) 


28., 
30.7 
(29.7) 


37-0 


7-3 


9.6 


10. 


11-3 


14. I 












14. S 


17.0 


17.8 


20. 


22. S 















In table in are the results of measurements at four chosen temperatures on four 
oysters. These experiments were all done within a few days after the oysters were 
taken from the beds and therefore serve to some extent as a control on the condition 
of the oysters used in the other series. The first columns of results show the decimilli- 
grams of oxygen used per hour at the designated temperatures. The averages of com- 
parable experiments are put in parentheses. The figures in the next four columns are 
obtained by computing the averages of the oxygen utilization per lOO grams of oyster. 
In the next column is the weight, in grams, of the shell contents of each oyster when 
dried to constant weight. The last four columns show average decimilligrams of oxygen 
used per gram of dried substance. The figures in these columns were corrected for the 



2l6 



BULI.ETIN OF THE BUREAU OF FISHERIES. 



oxygen used by the shells. The shells of each oyster were at the end of the observations 
carefully cleaned in sea water and then used for two or three measurements of their 
oxygen-absorbing power at different temperatures. As these results were obtained 
under the same conditions as those expressed in table in, they represent a fair estimate 
of the oxygen absorbed by the shells during measurements with the intact oyster. There 
is reason, as will be shown below, to believe that oxygen removed from the water in this 
way is not utilized by the active tissues of the oyster. It seems reasonable, therefore, 
to subtract the amount (measured or computed) of oxygen utilized by the shells from 
that used by the whole oyster before computing the oxygen requirements per gram of 
dried tissue. 

Table III. — Oxygen Used by Oysters. 

Note. — Figures in parentheses are averages of measurements under approximately uniform conditions. 





Dccimilligrams oi oxygen used 
per hour. 


Averages of same per hour per 
100 grams. 




Average dccimilligrams used per 
hour per gram of dried weight. 


"Weight. 
whole 
oyster. 










Weight, 
dried 
oyster. 




At 
20* to 
20.5 "C. 


At 

22° to 

2..5-C 


At 

24° to 

24.5° C. 


At 
26° to 
26.s°C. 


At 

20' to 

20.5° C. 


At 
22° to 

22.S°C. 


At 
24° to 
24.5°C. 


At 
26' to 
26.s°C. 


At 
20° to 

20.s'*C. 


At ' At 
22° to 24° to 

22.5°C 24.S°C. 


At 

26° to 
26.5°C. 


Grams. 


















Grams. 










47-8 


10. 6 


12.2 
14. I 
(i3-i) 


14.2 


17. I 




27.4 


29. 7 


35.7 


1. 15 


7.92 


9.74 


10.40 


12.90 


73-5 


16.6 


20- 

ah 


23.1 

18.3 

(20. r) 


22.0 


22.6 


23.0 


28.2 


30.0 


1.66 


8.20 


8.61 


9.43 


9.56 


153- o 


19- 4 


22.4 


21.4 
21.7 

24. s 

(22. 5) 


25-2 

25-9 

(25- 5) 


12. 7 


14.6 


14. 7 


16.6 


2.36 


5.98 


6.78 


6.56 


7-15 


173- o 


23-5 


24-5 


29.2 


39-0 


13.6 


14.2 


17.3 


2r. 2 


3.64 


3.49 


4.00 


4-53 


6. 10 


Average. 




24.7 

(24. 6) 


30.8 
(30. 0) 


,34-3 
(36. 6) 




















17-5 


19.7 


21.9 


25-3 


17.8 


20.3 


23.5 


25-9 




6.41 


7- 28 7. 73 


8.94 



A graphic representation of the oxygen utilization of oysters at different tempera- 
tures is given on page 217. The ordinates represent decimilligrams of oxygen used 
per hour and the abscissae are degrees Centigrade. The full lines represent measure- 
ments on intact oysters. Curve i is constructed from the averages of the oxygen utiliza- 
tion per hour per 100 grams in experiments on nine oysters as summarized in table 11. 
Curve II is constructed from similar averages of experimental results on four oysters as 
shown in table lu. Curve in is based on the same results used foi curve 11, but repre- 
sents the averages of oxygen used pei hour per gram ot dried shell contents. The rela- 
tionship between oxygen and temperature is apparently a simple one. The interrupted 
lines represent measurements on empty oyster shells showing the decimilligrams of 
oxygen used per hour by shells as recorded in table iv. Curves a, b, c, and d refer, 
respectively, to shells weighing 47.8, 73.4, 153, and 161 grams. The effect of tempera- 
ture on the three larger shells seems to be fairly constant; theii curves are parallel. 
The discrepancy in the smallest shell may be due to experimental error as so few deter- 
minations were made. 



OXYGEN REQUIREMENTS OF SHELLFISH. 



217 



26 




20^ sr ^2^ £3' ^^4^ ^s' jss' zrc. 



2l8 BULLETIN OF THE BUREAU OF FISHERIES. 

NON UTILIZATION OF OXYGEN BY CLOSED OYSTERS. 

Since oysters can close absolutely water tight, it seemed possible that under such 
conditions they would take in no oxygen. The very small oxygen requirements of 
voluntarily closed individuals could not, however, be interpreted as proof of this because 
when the oyster appears to be closed it may be slightly and invisibly open. This was 
proved by graphic records. To insure closure throughout an observation it was neces- 
sary, therefore, to use some artificial closing device. Several clamps were tried. An 
ordinary surgeon's artery clamp was found to be most satisfactory. If clamps without 
imperfections, carefully vaselined, were used, they did not appreciably rust during the 
experiment and withdrew from the water only a small and constant quantity of oxygen. 
As control experiments the oxygen absorption of empty shells of oysters about the same 
size as the one observed was measured. The control shells were fastened together by a 
clamp duplicating the one used on the oyster. Water had some access to the interior 
of the empty shells through nicks in their edges. On their immersion in water all air 
was driven from them. In many experiments controls were deferred until the same 
oyster could be emptied and its shells used for control measurements. 

The results of a number of determinations are given in table v. It is seen that in 
every case the experiment and its control are in close agreement, as the difference is 
within the limit of experimental error except in the case of the largest oyster used. 
Even these differences, however, show a larger oxygen absorption by the empty shells 
than by the closed intact oysters. That the slight oxygen disappearance does not repre- 
sent a respiratory intake by diffusion through the shells is indicated not only by the 
controls but by the obser^^ation that a two hours' exposure of the clamped oyster does 
not cause twice the oxygen absorption observed during one hour. Thus in one experi- 
ment a clamped oyster used 1.83 decimilligrams of oxygen in one hour, but 3.01 in two 
hours, while another, which used 1.70 decimilligrams in one hour, required 2.80 for two 
hours. 

The explanation of the constant slight absorption of oxygen by clamped oysters 
and empty shells was not positively determined, but would seem to lie in several 
causes. Bacteria and various marine vegetative growths on the shells were first con- 
sidered as possible oxygen users. Oyster shells that had been soaked 16 hours in 80 
per cent alcohol and then carefully scrubbed and dried, did, indeed, show a diminished 
oxygen absorbing capacity, in one case lowered from 5.25 decimilligrams per hour before 
the alcohol treatment to 4.68 after it, and in another, from 3.08 to 2.34. This indicates 
that foreign growths do not account for all the oxygen absorption, and, indeed, it was 
found that the cleanest and most carefully sterilized shells took oxygen from the water. 

An adsorption effect of porous substances on dissolved oxygen suggested itself as 
another possibility. It was found that porcelain evaporating dishes about the size 
of oysters showed equivalent oxygen absorbing powers. Corks had the same capacity. 
Water containing medium sized corks lost 2.34 decimilligrams of oxygen per hour, while 
in a control experiment water alone lost only 0.26 decimilligram, which is within the 
limit of experimental error. 



OXYGEN REQUIREMENTS OF SHELLFISH. 
Table IV. — Oxygen Absorbed by Empty Oyster Shells. 



219 





47-8 


47.8 


73-4 


73-4 


73-4 


iSi 


153 


161 


161 


Temperature of experiment in decree! centigrade. . 




J3.4 
1.9 


25-8 
2.4 


31.7 
3-6 


22.3 26.1 


22.0 
6.1 


25-8 21. s 


26. s 















Table V. — Oxygen Absorbed by Closed Oysters. 



Weight of 
oyster. 


Tempera- 
ture of 
experi- 
ment. 


' Oxygen 

used per 
hour. 


Description of control experiment. 




°C. 


Mgrjio. 




45 grams . . . 
Control 


22.0 
22.0 


1.70 
1.70 


Empty shells of same oyster with artery clamp. 


■;o grams. . . 
Control 


22.0 
22.0 


..83 
1.83 


Do. 


66.5 prams. . 

Control 

Control 


23-2 
21.0 
23- 2 


2.04 
1.92 
2.58 


Do. 

Empty shells of oyster weighmg 45 grams with clamp. 


66.5 grams. . 
Control 


20.5 
20.5 


i.4r 
1.48 


Empty shells of oyster weighing 51 grams with clamp. 


128 grams.. 
Control 


20. s 

20.5 


1.79 
1.92 


Empty shells of same oyster with artery clamp. 


147 grams. . 
Control 


20.5 
20.5 


1.74 
J. 62 


Do. 


244 grams . . 
Control 


20.5 
21.0 


1.70 
2-34 


Do. 


262 grams. . 
Control 


20.5 
21.0 


3-39 
4.68 


Do. 


244 grams. . 


27-5 


3-47 




128 grams. . 
66.5 grams.. 
76 grams. . . 


27-5 

27- S 
27-5 


2.36 
2.49 
2.80 


Control experiments not made. 



RESISTANCE OF OYSTERS TO LACK OF OXYGEN. 

A series of experiments was undertaken to find out the minimum oxygen supply 
that would maintain an oyster alive. The sea water surrounding an oyster in a vacuum 
desiccator was as far as possible rendered oxygen free by boiling at room temperature 
under diminished pressure for half an hour. It was found in two trials that sea water 
alone when so treated and kept twelve hours in the closed desiccator still had an oxygen 
content less than 0.5 of a part per million. An oyster kept under these circumstances 
four days showed no ill effects. Another was kept thus three days, transferred to a 
second desiccator of exhausted sea water, which was quickly again pumped out, and 
was then kept four days further in the oxygen poor medium. The shells then had some 
black deposits on them indicative of incipient anaerobic putrefaction. The sea water 
on opening the desiccator was found absolutely oxygen free. The oyster, however, 
seemed unimpaired, and after remaining in the aquarium some time was opened and 
found apparently entirely normal. As each desiccator held about 1,200 c. c. and the 
oxygen content of the water in each case was at the most 0.5 of a part per million, the 
oxygen available to the oyster might be estimated as 1.2 milligrams plus the small 
amount obtained during the transfer from one desiccator to the other. If we disregard 
the latter source because the oyster was tight closed at the time, only 1.2 milligrams of 
oxygen were used during seven days. 



220 



BULLETIN OF THE BUREAU OF FISHERIES. 



In another experiment an oyster was kept three days in the first desiccator full of 
pumped-out water, three days in the second, two days in the third, two days in the fourth, 
and two days in the fifth. By that time it was black and unable to close properly. 
After a few hours in the aquarium it showed disintegration, so that twelve days of life 
in oxygen-poor water proved fatal. Time and facilities for carrying out many of these 
experiments were missing, although the seven-day experiment was practically dupli- 
cated by one in which an oyster was kept in the same desiccator full of water six days 
with no ill effects. That the fatal effect of a twelve days' exposure was not due to 
insufficient renewal of the water was shown by control experiments in which several 
oysters were kept in the same water during fourteen days while air was bubbled through 
it. The oysters sur\dved this treatment uninjured. 

OXYGEN REQUIREMENTS OF CLAMS. 

Measurements on clams were made by the same method used for oysters. The 
results of successful experiments are embodied in table vi. They show a general agree- 
ment with measurements on oysters. The amount of oxygen used by ciams weighing 
about 60 grams is somewhat higher per 100 grams than that used by an oyster of about 
the same weight and observed at the same temperature. Computed per gram of dried 
shell contents, however, the oxygen requirements of the clam seem somewhat smaller 
than those of the oyster. Here, as with oysters, the amount of oxygen used is more 
or less proportional to increase in the temperature, though sufficient data to show a sim- 
ple relationship were not obtained. In this case, also, the oxygen requirement per gram 
is less in the larger individual than in the smaller, again like the oyster. 

Table VI. — Oxygen Used by Clams. 

Note. — Figures in parentheses are averages of measurements under approximately uniform conditions. 



Weight 
whole 
clam. 


Decimilligrams of oxygen used 
per hour. 


Averages of same per hour per 
100 grams. 


Weight 
dried 
clam. 


Average mgr/io used per hour 
per gram, dried weight. 


At 20° to 
21° c. 


At 22° to 
22.5° c. 


At 24° to 
24.5° c. 


At 20° to 

2I°C. 


At 22° to 

22.5° C. 


At 24* to 
24.5^ C. 


At 2o° to 
21° C. 


At 22° to 
22.5° C. 


At 24* to 
24.5^ C. 


Grams. 
7.0 

19. S 
21.0 

28.0 
57-0 

57- S 
60.0 
63.0 


I. 2 

C2-I) 

5. 19 

9-2 
6.7 
(7-9) 

S. 2 

II. 

12.4 

(ll-7) 






=9-6 

26.7 
26.9 

29-3 
20.7 






GrjjHJ. 








9-7 


15. 1 


49-7 


77-4 


1.32 


3.93 


7-35 


II. 4 


































17.2' 
19. 1 


30.0 


30.0 
31-9 


52.2 


3-97 




4.34 


7-5.'; 








I-- 7 

IS- 2 

(16.4) 




25-3 





























OXYGEN REQUIREMENTS OF SHELLFISH. 
Table VII. — Oxygen Absorbed by Closed Quahogs. 



221 





ISO 


150 


91 


91 


246 


246 


150 a 


ISO 6 


91 » 






24.0 
•37 


34.0 
■=S 


24- 
•38 


23- 
•25 


24-3 
•=3 


23- 
4^6o 


23^0 

4' 30 


23^6 

^•43 


23-5 
2-95 







a Voluntarily closed but not clamped. 



& Measurements on empty shells alone. 



OXYGEN ABSORPTION OF CLOSED CLAMS. 

Only one experiment was made in this connection. A medium-sized clam was 
closed by an artery clamp over the siphon end of the shells. As a control, empty shells 
of an oyster of the same size similarly clamped were used. The live clam absorbed 2.68 
decimilligrams of oxygen per hour at a temperature of 23.5° C, while the shell took 2.58. 
This indicates that the clam, like the oyster, has little or no opportunity to obtain oxygen 
when the shell is not open. Further observations incidentally made confirm this con- 
clusion. A medium-sized clam which visibly failed to open throughout an experiment 
to determine its oxygen requirements took only 2.44 decimilligrams of oxygen from the 
water in an hour. Other similar results were obtained. 

OXYGEN REQUIREMENTS OF QUAHOGS. 

Great difficulty was experienced in measuring the oxygen utilization of quahogs, 
because they seldom opened for any length of time under the conditions of experimen- 
tation. As a result of this, only a few measurements that could be considered reliable 
were obtained. It was found necessary to place the specimen in sea water in the desic- 
cator a long time before the experiment, usually the night before, in order to have it 
open at the time of observation. Handling or moving caused it to close and stay closed 
for some hours. 

The few successful observations showed a rather low oxvgen utilization. One 
specimen weighing 91 grams used, at 24° C, 10. i decimilligrams of oxygen in one hour, 
10.8 in another measurement, and 6.4 in a third. Another quahog, weighing 150 grams, 
used, at 24° C, 7.8 decimilligrams per hour, and a large one (470 grams) used 22.4 deci- 
milligrams per hour. Many other measurements were attempted, but owing to closure 
soon after the beginning of observation were unreliable. The oxygen requirements in 
proportion to the dried weight showed a still greater discrepancy in comparison with 
similar computations for the oyster. The dried weights of the shell contents of the 
first two quahogs observed were, respectively, 2.22 grams and 3.86 grams. The oxygen 
used per hour and per gram of dried weight, then, was 4.10 decimilligrams for the first 
and 2.21 for the second. This is less than half the amount of oxygen used bv ovsters 
of comparable weight obser\'ed at the same temperature. To prop the shells open 
seemed hardly worth while, because the oxygen utilization under such circumstances 
would be abnormal on account of the resulting violent contractions of adductor muscles. 
It seemed best, therefore, to be content with the conclusion that under the circumstances 
of these experiments quahogs used only a small quantity of oxygen. 



222 



BUIylvETIN OF THE BUREAU OF FISHERIES. 



UTILIZATION OF OXYGEN BY CLOSED OUAHOGS. 

Clamping these shells as in the experiments described for oysters showed that closed 
quahogs used no oxygen. Their very smooth shells apparently took almost no oxygen 
from the water. With various sizes of quahogs clamped and observed at 24° C, results 
were obtained as follows: 0.37, 0.25, 0.38, 0.23, and 0.25 decimilligram of oxygen per 
hour. The empty shells, considerably broken in the process of opening, used a 
distinctly larger amount of oxygen than did the closed intact animal. The small amounts 
of oxygen taken up under these conditions are no more than would disappear from the 
sea water with a clamp in it. 

It was clearly shown, however, that voluntarily closed quahogs did take up appre- 
ciable quantities of oxygen. In observations where the shells were apparently quite 
closed, various medium and large sized specimens took up, at 24° C, 2.9, 6.1, 4.6, and 
4.3 decimilligrams of oxygen per hour. It would seem, then, that when voluntarily 
closed they do not remain shut absolutely tight, but take in small amounts of water 
through an aperture too narrow to be visible to the naked eye. The results are sum- 
marized in table vii. 

CONCLUSIONS. 



1. Oysters of medium sizes, at temperatures between 19° and 28° C, used from 7 to 
35 decimilligrams of oxygen per hour per 100 grams of entire weight. The amount varies 
with the temperature, so far as experiments show, according to simple relationship, so 
that the curve approximates a straight line. It is proportionally less for larger speci- 
mens. The oxygen utilization is, however, exceedingly variable, depending on a variety 
of conditions, most of which probably affect the openness of the shell. 

2. Oysters when tightly closed take no oxygen from the surrounding water; at 
least, no more than is taken by empty shells. 

3. Oysters show considerable resistance to lack of oxygen. Only exposure for more 
than a week to water containing very small quantities of oxygen proved fatal. This 
indicates that any conditions causing temporary decrease in the available oxygen are not 
a significant factor in oyster culture. 

4. The common clam (Mya arenaria) shows a higher oxygen requirement than the 
oyster. This seems surprising, in view of the fact that clams so often exist in muds 
where oxygen-consuming putrefactions are going on. The oxygen requirements of 
clams and oysters in proportion to their dried weights are about equal. 

5. Both clams and quahogs (Vcmts merccnaria) use no oxygen from the water when 
tightly closed, but the quahog takes up oxygen while slightly and invisibly open. 

6. The oxygen requirements of the quahog are, under the conditions of these' experi- 
ments, conspicuously low. 



UBRARVOFCOHGJ^S 





